This invention relates to compressor bleeds for turbine type power plants and particularly to means for correcting for error in the sensed parameters occasioned by a change in engine geometry.
All axial flow compressors of gas turbine power plants have the propensity to surge or stall under certain operating conditions. While stall and surge are not completely understood, suffice it to say, that under certain conditions the flow separates from the airfoil section of the compressor blade causing a pressure pulsation setting up a vibratory condition which ultimately, not only leads to deterioration of the efficiency of the compressor but may cause damage to the engine itself.
It is well known in the art to provide means for bleeding the compressor section of an axial flow compressor of the turbine type power plant by either scheduling the bleed valve at a function of a predetermined operating parameter or merely holding the bleed valves opened during engine start-up. As for example, the steady state bleed control described herein is exemplary of a system for scheduling the bleed valve. It will be noted by referring to FIG. 2 that the scheduled bleed control opens the bleed valve below a predetermined corrected speed (N/.sqroot..theta.) and closes the bleed valve between a given corrected speed value and maintains the valve closed beyond this value.
The problem solved by this invention is to assure that when the bleed valves open and the airflow diverted from the engine imposes an error on the signal sensed to actuate the surge valve reflecting the change in engine geometry. Hence, if the signal, such as compressor discharge pressure (CDP) is sensed to indicate acceleration or deceleration of the engine, the opening of the bleed valve would not be a true reflection of these conditions. The unwanted signal or error signal occasioned by changing engine geometry are isolated so that CDP is indicative solely of acceleration and deceleration.